1. Field of the Invention:
The present invention relates to a method of machining a lost foam pattern which is to be used in full-mold casting to produce a mold.
2. Description of the Relevant Art:
In full-mold casting, an expendable foam pattern in the same shape as a mold to be produced is placed in foundry sand such as resin sand or the like, and molten metal is poured into the foam block. The foam block is vaporized by the poured molten metal, which is then cast as a mold having a shape identical to that of the foam block.
To manufacture such a foam pattern, a foam block is cut to a desired shape usually with a vertical open-type machine tool. The vertical open-type machine tool has a cutter head positioned above a foam block as a workpiece that is positioned on a workpiece table. The cutter head is moved based on NC data to cut an upper surface of the workpiece to a desired shape.
After the upper surface of the workpiece has been cut, the workpiece on the workpiece table is inverted, and a lower surface thereof is cut by the cutter head.
Since the cutter head is required to be positioned upwardly of the workpiece, the vertical open-type machine tool is relatively large in size as it needs a rigid mount base for supporting the cutter head. The vertical open-type machine tool is also complex because it is necessary to invert the workpiece manually or with a workpiece inverting device. Furthermore, inasmuch as the workpiece is cut at its upper surface, chips produced from the workpiece by the cutter head tend to be accumulated around the machined region around the upper surface of the workpiece, making the working environment less than optimum. The environmental sanitary conditions for the operator of the machine tool are lowered by scattered chips from the workpiece.
A machining apparatus capable of machining upper, lower, and side surfaces of a workpiece is known from Japanese laid-open patent publication No. 2-109663, for example. The disclosed apparatus has a box surrounding a workpiece. The workpiece is machined within the box so that chips and cutting oil are prevented from being scattered around. When an upper surface of the workpiece is machined, however, chips tend to accumulate on the upper surface of the workpiece and cannot fully be removed therefrom.
According to the conventional machining apparatus, in addition, since all necessary surfaces of a workpiece are machined on one machine tool, the time in which the machine tool is occupied by one workpiece is so long that the yield of machined workpieces is low. Stated otherwise, until a workpiece mounted on a workpiece table is fully machined and removed from the workpiece table, a next workpiece cannot be supplied to and clamped in the machine tool.
There has been a demand for a machining system capable of machining workpieces smoothly along a series of machining steps with a reduced expenditure of manual labor for an increased rate of production.